Combination capacitive and resistive obstacle sensor

ABSTRACT

An obstacle sensor for a closure panel of a vehicle includes an elongate non-conductive case which encloses a first, second, and third elongate conductive electrodes. The first and second electrodes are separated by a portion of the case, with a capacitance between the first and second electrodes changing when an obstacle approaches the first electrode. The changed capacitance of the obstacle sensor provides a proximity indication of the obstacle to the obstacle sensor. The second and third electrodes are separated by an air gap formed in the case, with a resistance between the second and third electrodes changing when the second and third electrodes come into contact upon compression of the case by the obstacle. The changed resistance of the obstacle sensor provides a contact indication of the obstacle with the obstacle sensor.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. Ser. No. 14/766,937 filedAug. 10, 2015, now U.S. Pat. No. 9,477,003 issued Oct. 25, 2016, whichis a National Stage of International Application No. PCT/IB2014/001117filed Mar. 14, 2014, which claims the benefit and priority to U.S.provisional patent application Ser. No. 61/791,472 filed on Mar. 15,2013. The entire disclosures of each of the above applications areincorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to the field of obstacle sensors, and morespecifically, to a combination capacitive and resistive obstacle sensorfor use in vehicles and other devices.

BACKGROUND

In motor vehicles such as minivans, sport utility vehicles and the like,it has become common practice to provide the vehicle body with a largerear opening. A liftgate (also referred to as a tailgate) is typicallymounted to the vehicle body or chassis with hinges for pivotal movementabout a transversely extending axis between an open position and aclosed position. Typically, the liftgate may be operated manually orwith a power drive mechanism including a reversible electric motor.

During power operation of a vehicle liftgate, the liftgate mayunexpectedly encounter an object or obstacle in its path. It istherefore desirable to cease its powered movement in that event toprevent damage to the obstacle and/or to the liftgate by pinching of theobstacle between the liftgate and vehicle body proximate the liftgatehinges.

Obstacle sensors are used in such vehicles to prevent the liftgate fromclosing if an obstacle (e.g., a person, etc.) is detected as theliftgate closes. Obstacle sensors come in different forms, includingnon-contact or proximity sensors and contact sensors (e.g., pinchsensors) which rely on physical deformation caused by contact with anobstacle. Non-contact or proximity sensors are typically based oncapacitance changes while contact sensors are typically based onresistance changes.

Non-contact sensors typically include a metal strip or wire which isembedded in a plastic or rubber strip which is routed along and adjacentto the periphery of the liftgate. The metal strip or wire and thechassis of the vehicle collectively form the two plates of a sensingcapacitor. An obstacle placed between these two plates changes thedielectric constant and thus varies the amount of charge stored by thesensing capacitor over a given period of time. The charge stored by thesensing capacitor is transferred to a reference capacitor in order todetect the presence of the obstacle.

Contact sensors are typically applied in the form of a rubber stripwhich is routed along and adjacent to the periphery of the liftgate. Therubber strip embeds two wires which are separated by an air gap. Whenthe two wires contact one another, the electrical resistancetherebetween drops, and a controller connected to the two wires monitorsthe drop in resistance, detecting an object when the drop exceeds apredetermined threshold. One problem with such contact sensors, however,is that they have a limited activation angle typically on the order ofabout thirty five degrees. Thus, in the event the pinch force is appliedobliquely rather than head on, the wires may not contact one another.

A need therefore exists for an improved obstacle sensor for use invehicles and other devices. Accordingly, a solution that addresses, atleast in part, the above and other shortcomings is desired.

SUMMARY OF THE INVENTION

According to one aspect of the invention, there is provided an obstaclesensor, comprising: an elongate non-conductive case enclosing first,second, and third elongate conductive electrodes; the first and secondelectrodes being separated by a portion of the case, a capacitancebetween the first and second electrodes changing when an obstacleapproaches the first electrode to provide a proximity indication; and,the second and third electrodes being separated by an air gap formed inthe case, a resistance between the second and third electrodes changingwhen the second and third electrodes come into contact upon compressionof the case by the obstacle to provide a contact indication.

BRIEF DESCRIPTION OF THE DRAWINGS

Features and advantages of the embodiments of the present invention willbecome apparent from the following detailed description, taken incombination with the appended drawings, in which:

FIG. 1 is rear perspective view illustrating an obstacle sensing systemfor a liftgate of a vehicle in accordance with an embodiment of anaspect of the invention;

FIG. 2 is a block diagram illustrating the obstacle sensing system ofFIG. 1 in accordance with an embodiment of an aspect of the invention;

FIG. 3 is a cross sectional view illustrating an obstacle sensor inaccordance with an embodiment of an aspect of the invention;

FIG. 4 is a wiring diagram illustrating connection of an obstacle sensorto a controller in accordance with an embodiment of an aspect of theinvention;

FIG. 5 is a cross sectional view illustrating an obstacle sensor mountedon a liftgate in accordance with an embodiment of an aspect of theinvention; and,

FIG. 6 is a flow chart illustrating operations of modules within anobstacle sensing system for detecting contact with or proximity of anobstacle, in accordance with an embodiment of an aspect of theinvention.

It will be noted that throughout the appended drawings, like featuresare identified by like reference numerals.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

In the following description, details are set forth to provide anunderstanding of the invention. In some instances, certain circuits,structures and techniques have not been described or shown in detail inorder not to obscure the invention.

FIG. 1 is rear perspective view illustrating an obstacle sensing system10 for a liftgate 12 of a vehicle 14 in accordance with an embodiment ofan aspect of the invention. And, FIG. 2 is a block diagram illustratingthe obstacle sensing system 10 of FIG. 1 in accordance with anembodiment of an aspect of the invention. The obstacle sensing system 10is shown operatively associated with a closure panel 12 of a motorvehicle 14. According to one embodiment, the closure panel is a liftgate12. It will be understood by those skilled in the art that the obstaclesensing system 10 may be used with other closure panels and windows of avehicle or other device.

The liftgate 12 is mounted to a body 16 of the motor vehicle 14 througha pair of hinges 18 to pivot about a transversely extending pivot axiswith respect to a large opening 500 (see FIG. 5) in the rear of the body16. The liftgate 12 is mounted to articulate about its hinge axisbetween a closed position where it closes the opening 500 and an openposition where it uncovers the opening 500 for free access to thevehicle body interior and assumes a slightly upwardly angled positionabove horizontal. The liftgate 12 is secured in its closed position by alatching mechanism (not shown). The liftgate 12 is opened and closed bya drive mechanism 20 with the optional assist of a pair of gas springs21 connected between the liftgate 12 and the body 16. The drivemechanism 20 may be similar to that described in PCT InternationalPatent Application No. PCT/CA2012/000870, filed Sep. 20, 2012, andincorporated herein by reference. The drive mechanism 20 may be orinclude a powered strut as described in U.S. Pat. No. 7,938,473, issuedMay 20, 2011, and incorporated herein by reference.

According to one embodiment, the obstacle sensing system 10 includes twoobstacle sensors 22, a mounting channel or track 24 for each of thesensors 22, and a controller 26. The pair of sensors 22 are positionedproximate to laterally opposing sides 28 and 30 of the liftgate 12. Bothof the sensors 22 include an upper end in close proximity to an upperlateral edge 32 of the liftgate 12. The sensors 22 extend downwardlyfrom their upper ends along a substantial portion of the liftgate 12.The sensors 22 are both electrically attached to a wire harness 430adapted to plug into the controller 26. The controller 26 controls thedrive mechanism 20 to open the liftgate 12 in the event it receives anelectrical signal from one or more of the sensors 22.

According to one embodiment, each of the sensors 22 is mounted to theliftgate 12 through a mounting track 24. The mounting tracks 24 may besubstantial mirror images of one another. For this reason, only one ofthe mounting tracks 24 needs to be described herein. The mounting track24 provides a mounting surface for the sensor 22 which can deflect afterthe sensor 22 compresses and sends a control signal to the controller26. This deflection allows the controller 26 sufficient time to reversethe drive mechanism 20 without damaging the obstacle, the liftgate 12 orthe drive mechanism 20. The mounting track 24 also provides a graduallychanging surface to which the sensor 22 may be mounted. According to oneembodiment, the sensors 22 are mounted to the mounting tracks 24, whichare in turn attached to the liftgate 12. Alternatively, it will beunderstood that in certain applications it may be desirable to mount thesensors 22 and their associated tracks 24 on the body 16 of the vehicle14 adjacent to the liftgate 12.

In operation, when the liftgate 12 contacts or approaches an obstacleproximate to the sensor 22 as it is articulated towards its closedposition, the sensor 22 is activated. The activation of the sensor 22 isdetected by the controller 26. In response, the controller 26 reversesthe drive mechanism 20 to articulate the liftgate 12 to its openposition.

The drive mechanism 20 is controlled in part by the obstacle sensingsystem 10. The obstacle sensing system 10 includes elongate sensors 22that help prevent the liftgate 12 from pinching or crushing an obstaclesuch a person's finger (not shown) that may be extending through theopening 500 when the liftgate 12 lowers towards or nears its closedposition. It will be appreciated by those skilled in the art that theobstacle sensing system 10 may be applied to any motorized or automatedclosure panel structure that moves between an open position and a closedposition. For example, a non-exhaustive list of closure panels includeswindow panes, sliding doors, tailgates, sunroofs and the like. Forapplications such as window panes or sun roofs, the elongate sensors 22may be mounted on the body 16 of the vehicle 14, and for applicationssuch as powered liftgates and sliding doors the elongate sensor 22 maybe mounted on the closure panel itself, e.g., at the leading edge of asliding door or the side edges of a liftgate 12.

FIG. 3 is a cross sectional view illustrating an obstacle sensor 22 inaccordance with an embodiment of an aspect of the invention. FIG. 4 isacross sectional view illustrating an obstacle sensor 22 mounted on aliftgate 12 in accordance with an embodiment of an aspect of theinvention. And, FIG. 5 is a wiring diagram illustrating connection of anobstacle sensor 22 to a controller 26 in accordance with an embodimentof an aspect of the invention.

The obstacle sensor 22 is a hybrid three electrode sensor that allowsfor both a resistive mode and a capacitive mode of obstacle detection.In general, the resistive mode operates through the middle (second) andlower (third) electrodes 2, 3. The capacitive mode operates through theupper (first) and middle (second) electrodes 1, 2 and/or with all threeelectrodes 1, 2, 3. In capacitive mode, the upper and middle electrodes1, 2 function in a driven shield configuration (i.e., with the middleelectrode 2 being the driven shield) with the lower electrode 3 being anoptional ground. The case 300 positions the three electrodes 1, 2, 3 inan arrangement that facilitates operation of the sensor 22 in both acapacitive mode and a resistive mode.

In capacitive mode, the upper electrode 1 (optionally comprising aconductor 1 a embedded in conductive resin 1 b) acts as a capacitivesensor electrode, and the middle electrode 2 (optionally comprising aconductor 2 a embedded in conductive resin 2 b) acts as a capacitiveshield electrode. A dielectric 320 (e.g., a portion 320 of the case 300)is disposed between the middle electrode 2 and the upper electrode 1 toisolate and maintain the distance between the two. The controller (orsensor processor (“ECU”)) 26 is in electrical communication with theelectrodes 1, 2 for processing sense data received therefrom.

In resistive mode, the middle electrode 2 acts as an upper resistiveelement and the lower electrode 3 acts as a lower resistive element. Asbest shown in FIG. 4, the middle and lower electrodes 2, 3 are connectedat one end of the sensor 22 to a pre-determined resistor 421 and at theother end to a wire harness 430 and the controller 26. The middle andlower electrodes 2, 3 are separated by an air gap 330 formed within thecase 300 and bounded by compressible or deflectable spring side walls301, 302 of the case 300. When an obstacle contacts the sensor 22 withenough force and within the activation angle range of the sensor 22, itdeflects the upper portion of the sensor 22 and brings the middle andlower electrodes 2, 3 into contact. This lowers the resistance of thesensor 22 to a level that is detectable by the controller 26 which is inelectrical communication with the middle and lower electrodes 2, 3 forprocessing sense data received therefrom.

According to one embodiment, the obstacle sensor 22 includes an elongatenon-conductive case 300 having three elongate conductive electrodes 1,2, 3 extending along its length. The electrodes 1, 2, 3 are encapsulatedin the case 300 and are normally spaced apart. When the sensor 22 iscompressed in a direction substantially parallel to its length by anobstacle, the middle and lower electrodes 2, 3 make contact so as togenerate an electrical signal indicative of contact with the obstacle.When an obstacle comes between the tailgate 12 and the body 16 ofvehicle 14, it effects the electric field generated by the upperelectrode 1 which results in a change in capacitance between the upperand middle electrodes 1, 2 which is indicative of the proximity of theobstacle to the liftgate 12. Hence, the middle and lower electrodes 2, 3function as a resistive contact sensor while the upper and middleelectrodes 1, 2 function as a capacitive non-contact or proximitysensor.

According to one embodiment, the upper (first) electrode 1 may include afirst conductor 1 a embedded in a first partially conductive body 1 b,the middle (second) electrode 2 may include a second conductor 2 aembedded in a second partially conductive body 2 b, and the lower(third) electrode 3 may include a third conductor 3 a embedded in athird partially conductive body 3 b. The conductors 1 a, 2 a, 3 a may beformed from a metal wire. The partially conductive bodies 1 b, 2 b, 3 bmay be formed from a conductive resin. And, the case 300 may be formedfrom a non-conductive (e.g., dielectric) material (e.g., rubber, etc.).Again, the upper electrode 1 is separated from the middle electrode 2 bya portion 320 of the case 300. The middle electrode 2 is separated fromthe lower electrode 3 by an air gap 330 formed in the case 300.

According to one embodiment, the obstacle sensor 22 is mounted on theliftgate 12 as shown in FIGS. 1 and 5. The sensor 22 may be fastened tothe liftgate 12 by an adhesive tape 340 provided along the base of thesensor's case 300.

According to one embodiment, the case 300 may be formed as an extruded,elongate, elastomeric trim piece with co-extruded conductive bodies 1 b,2 b, 3 b and with the conductors 1 a, 2 a, 3 a molded directly into thebodies 1 b, 2 b, 3 b. The trim piece may be part of the liftgate watersealing system, i.e., form part of a seal, it may form part of thedecorative fascia of the vehicle 14, or it may form part of the interiortrim of the liftgate 12.

As shown in FIG. 4, a capacitive sensor circuit 410 is formed by thecapacitive sensor electrode 1, a first terminal resistor 411, and thecapacitive shield/upper resistive sensor electrode 2. In addition aresistive sensor circuit 420 is formed by the capacitive shield/upperresistive sensor electrode 2, a second terminal resistor 421, and thelower resistive sensor electrode 3. The resistors 411, 421 arediagnostic resistors for the sensor circuits 410, 420. Both thecapacitive sensor circuit 410 and the resistive sensor circuit 420 arecoupled to and driven by the controller 26.

With respect to resistive sensing, the air gap 330 electricallyinsulates the middle electrode 2 and the lower electrode 3. However, thespring side walls 301, 302 of the sensor case 300 are flexible enough toenable the outer surfaces 2 c, 3 c of the partially conductive bodies 2b, 3 b of the two electrodes 2, 3 to touch one another when the sensor22 is compressed (e.g., as a result of a pinch event). The flexibilityof the sensor 22 may be controlled by its cross sectional configuration,including controlling the thickness of the side walls 301, 302 of thecase 300 and the thickness of the partially conductive bodies 2 b, 3 b.The outer surfaces 2 c, 3 c of the partially conductive bodies 2 b, 3 bare shaped to increase the activation angle (i.e., the angle from thenormal at which a compressive or pinch force is applied to the sensor22) of the sensor 22. According to one embodiment, the outer surface 2 cof the middle electrode 2 may have a ball shape and the outer surface 3c of lower electrode 3 may have a socket shape as shown in FIG. 3.

The controller 26 measures the resistance (or resistance value) betweenthe middle electrode 2 and the lower electrode 3. The resistance will belarge in magnitude when the partially conductive bodies 2 b, 3 b areseparated from each other by the air gap 330, and will reduce inmagnitude if a portion of the partially conductive bodies 2 b, 3 bcontact one another when the sensor 22 is compressed. This drop inmeasured resistance is indicative of contact with an obstacle (i.e., apinch event).

With respect to capacitive sensing, a portion 320 of the case 300electrically insulates the upper electrode 1 and the middle electrode 2so that electrical charge can be stored therebetween in the manner of aconventional capacitor. According to one embodiment, the inner surface 2d of the middle electrode 2 may be shaped to improve the shieldingfunction of the middle electrode 2. According to one embodiment, theinner surface 2 d may be flat as shown in FIG. 3.

The sensor 22 is used by the controller 26 to measure a capacitance (orcapacitance value) of an electric field extending through the opening500 under the liftgate 12. According to one embodiment, the middleelectrode 2 functions as a shielding electrode since it is positionedcloser to the sheet metal of the liftgate 12. As such, the electricfield sensed by the upper electrode 1 will be more readily influenced bythe closer middle electrode 2 than the vehicle sheet metal. To improvesignal quality, the liftgate 12 may be electrically isolated from theremainder of the vehicle 14. A powered sliding door, for example, may beisolated through the use of non-conductive rollers.

The capacitance (or capacitance value) of the sensor 22 is measured asfollows. The capacitive sensor electrode 1 and the capacitiveshield/upper resistive sensor electrode 2 are charged by the controller26 to the same potential using a pre-determined pulse train. For eachcycle, the controller 26 transfers charge accumulated between theelectrodes 1, 2 to a larger reference capacitor (not shown), and recordsan electrical characteristic indicative of the capacitance of the sensor22. The electrical characteristic may be the resultant voltage of thereference capacitor where a fixed number of cycles is used to charge theelectrodes 1, 2, or a cycle count (or time) where a variable number ofpulses are used to charge the reference capacitor to a predeterminedvoltage. The average capacitance of the sensor 22 over the cycles mayalso be directly computed. When an obstacle enters the opening 500 underthe liftgate 12, the dielectric constant between the electrodes 1, 2will change, typically increasing the capacitance of the sensor 22 andthus affecting the recorded electrical characteristic. This increase inmeasured capacitance is indicative of the presence of the obstacle(i.e., its proximity to the liftgate 12).

FIG. 6 is a flow chart generally illustrating 600 a method of operatinga resistance module and a capacitance module within an obstacle sensingsystem 10 for detecting contact with or proximity of an obstacle, inaccordance with an embodiment of an aspect of the invention. Accordingto one embodiment, as shown in FIG. 6, the obstacle sensing system 10may use both capacitive and resistive sensing modes to detect contactwith or proximity of an obstacle. Software modules within the controller26 may toggle between resistive and capacitive sensing operations. Forexample, the method beings by 602 initializing the sensor 22 or sensors22 of the obstacle sensing system 10, followed by an 604 initiation of asample timer. The sample time can include a predetermined cycle time,such as seconds, in which to check the capacitive and sensing modes ofthe sensor(s) 22. Once the sample timer has been initiated, the methodproceeds by 606 checking the resistive sensor mode of the sensor 22. Ifa change in the resistance between the second and third electrodes 2, 3is detected, the method proceeds to 608 initiate a “REVERSAL COMMAND” tothe drive mechanism to cease a closing movement of the closure panel. Ifno change in the resistance between the second and third electrodes 2, 3is detected, the method proceeds by 610 checking the capacitive sensormode of the sensor 22. If a change in a capacitance between the firstand second electrodes 1, 2 is detected, the method proceeds to 608initiate a “REVERSAL COMMAND” to the drive mechanism to cease a closingmovement of the closure panel. If no change in the capacitance betweenthe first and second electrodes 1, 2 is detected, the method proceeds to602 re-initiate the sample timer.

The above embodiments contribute to an improved obstacle sensor 22 andprovide one or more advantages. First, by detecting proximity of anobstacle by capacitive sensing, overloading of the sensor 22 and thepinched obstacle during the time lag encountered by the powered openingof the liftgate 12 is reduced. Second, the sensor 22 allows for the useof resistive contact sensing as a back-up to capacitive proximitysensing.

The foregoing description of the embodiments has been provided forpurposes of illustration and description. It is not intended to beexhaustive or to limit the disclosure. Individual elements or featuresof a particular embodiment are generally not limited to that particularembodiment, but, where applicable, are interchangeable and can be usedin a selected embodiment, even if not specifically shown or described.The same may also be varied in many ways. Such variations are not to beregarded as a departure from the disclosure, and all such modificationsare intended to be included within the scope of the disclosure.

What is claimed:
 1. An closure system for a motor vehicle comprising: aclosure panel pivotably mounted to a body of the vehicle for movementbetween open and closed positions; and an obstacle sensing systemincluding an obstacle sensor having an elongate non-conductive caseenclosing a first, second, and third elongate conductive electrodes,said first and second electrodes being separated by a portion of saidcase, a capacitance between said first and second electrodes changingwhen an obstacle approaches said first electrode to provide a proximityindication of the obstacle to the obstacle sensor, and said second andthird electrodes being separated by an air gap formed in the case, aresistance between said second and third electrodes changing when thesecond and third electrodes come into contact upon compression of thecase by the obstacle to provide a contact indication of the obstaclewith the obstacle sensor, wherein said second and third electrodes arebounded by compressible spring side walls of said case to allow saidsecond and third electrodes to contact one another when the obstaclesensor is contacted by the obstacle.